Organic electroluminescent device with carrier blocking layer interposed between two emitting layers

ABSTRACT

An organic electroluminescent device including in sequence an anode, a first emitting layer ( 5 ), a carrier barrier layer ( 6 ), a second emitting layer ( 7 ) and a cathode stacked; wherein the ionization potential of the carrier barrier layer ( 6 ) is more than the ionization potential of the first emitting layer ( 5 ) by 0.1 eV or more and the affinity level of the carrier barrier layer ( 6 ) is less than the affinity levels of the first emitting layer ( 5 ) and the second emitting layer ( 7 ) by 0.1 eV or more.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of prior U.S. patentapplication Ser. No. 10/575,092, the disclosure of which is incorporatedby reference in its entirety. U.S. Ser. No. 10/575,092 is a NationalStage of PCT/JP05/04486 filed on Mar. 15, 2005 which claims the benefitof priority under 35 U.S.C §119 from Japanese Patent Application No.2004-088463, filed Mar. 25, 2004, the disclosures of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The invention relates to an organic electroluminescent device(hereinafter referred to as organic EL device).

BACKGROUND ART

Recently, white organic EL devices are being actively developed becausethey can be used for a mono-color display device, a lighting apparatussuch as a back light, and a full-color display with color filters. Inthe case where white organic EL devices are used for lightingapplications, they are required to have a high luminous efficiency, forexample, which is equivalent to or more than that of fluorescent lamps.

Many methods of producing white light emission by an organic EL devicehave been disclosed. Few of the methods produce white light with onlyone kind of emitting material and a single organic EL device generallyuses two or more kinds of emitting materials that emit lightsimultaneously. In the case of using two kinds of emitting materials, ablue emitting material and a yellow-to-red emitting material,yellow-to-red being the complementary color to blue, are selected.However, the yellow-to-red light emission becomes dominant in manycases, thereby yielding a reddish white color.

JP-A-2003-272857 proposes a white organic EL device in which thetendency for red to be strong in emitted light is negated by using ablue emitting layer as an emitting layer on the anode side, the emissionrange of which tends to be offset in the type where an emitting layer isdivided into two layers, and whose color change is suppressed. The levelof the luminous efficiency was, however, not necessarily enough.

Further, JP-A-08-078163 discloses a structure having acarrier-recombination-region-control layer interposed between a holetransporting layer and an electron-transporting layer, in which there isobtained white emission having luminous efficiency that is high to someextent although it is not necessarily at a practically sufficient level.Since, however, the affinity level of the abovecarrier-recombination-region-control layer has a large value relative tothe affinity level of the hole transporting layer, the driving voltageis high, and with the passage of the driving time, it comes to bedifficult to inject electrons into the hole transporting layer. As aresult, the blue emission intensity is decreased, and the emission isliable to be shifted toward red light.

It is an object of the invention to provide an organic EL device with ahigh luminous efficiency and small change in chromaticity.

DISCLOSURE OF THE INVENTION

Through research for solving the foregoing subjects, the inventors foundthat an organic EL device with a high luminous efficiency and smallchange in chromaticity can be obtained by interposing an electronbarrier layer between two organic emitting layers and controlling theenergy levels thereof, and completed the invention.

The invention provides the following organic EL device.

1. An organic electroluminescent device comprising in sequence an anode,a first emitting layer, a carrier barrier layer, a second emitting layerand a cathode stacked;

wherein the ionization potential of the carrier barrier layer is morethan the ionization potential of the first emitting layer by 0.1 eV ormore and the affinity level of the carrier barrier layer is less thanthe affinity levels of the first emitting layer and the second emittinglayer by 0.1 eV or more.

2. The organic electroluminescent device according to 1, wherein theionization potential of the carrier barrier layer is more than theionization potential of the first emitting layer by 0.2 eV or more andthe affinity level of the carrier barrier layer is less than theaffinity levels of the first emitting layer and the second emittinglayer by 0.2 eV or more.3. An organic electroluminescent device comprising in sequence an anode,a first emitting layer, a first carrier barrier layer, a second carrierbarrier layer, a second emitting layer and a cathode stacked;

wherein the ionization potential of the first carrier barrier layer ismore than the ionization potential of the first emitting layer by 0.1 eVor more and the affinity level of the second carrier barrier layer isless than the affinity level of the second emitting layer by 0.1 eV ormore.

4. The organic electroluminescent device according to 3, wherein theionization potential of the first carrier barrier layer is more than theionization potential of the first emitting layer by 0.2 eV or more andthe affinity level of the second carrier barrier layer is less than theaffinity level of the second emitting layer by 0.2 eV or more.5. The organic electroluminescent device according to any one of 1 to 4,wherein the first emitting layer comprises a first dopant for a firstemission color and the second emitting layer comprises a second dopantfor a second emission color.6. The organic electroluminescent device according to any one of 1 to 5,wherein at least one carrier barrier layer comprises a third dopant fora third emission color.7. The organic electroluminescent device according to any one of 1 to 6,wherein the first, second and third dopants are selected from blue,green or red.8. The organic electroluminescent device according to any one of 1 to 7,wherein the first emitting layer emits blue or red light.9. The organic electroluminescent device according to any one of 1 to 7,wherein the second emitting layer emits blue or red light.10. The organic electroluminescent device according to any one of 1 to7, wherein one of the first emitting layer and the second emitting layeremits blue light, and the other emitting layer emits red light.11. The organic electroluminescent device according to any one of 1 to10, wherein the first emitting layer comprises a hole-transportingmaterial and the second emitting layer comprises anelectron-transporting material.12. The organic electroluminescent device according to any one of 1 to11, wherein the hole mobility of the first emitting layer is 10⁻⁵cm²/v·s or more and the electron mobility of the second emitting layeris 10⁻⁶ cm²/v·s or more.13. The organic electroluminescent device of any one of 1 to 11 thatemits white light.

According to the invention, there can be provided an organic EL device,particularly a white organic EL device, with a high luminous efficiencyand small change in chromaticity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the constitution of a white organic ELdevice of Embodiment 1.

FIG. 2 is an energy level diagram of a first emitting layer, an electronbarrier layer and a second emitting layer in Embodiment 1.

FIG. 3 is a diagram showing the constitution of a white organic ELdevice of Embodiment 2.

FIG. 4 is an energy level diagram of a first emitting layer, a firstelectron barrier layer, a second electron barrier layer and a secondemitting layer in Embodiment 2.

FIG. 5( a) is an energy level diagram in Example 1, FIG. 5( b) is anenergy level diagram in Comparative Example 2, FIG. 5( c) is an energylevel diagram in Comparative Example 3, and FIG. 5( d) is an energylevel diagram in Comparative Example 4.

BEST MODES FOR WORKING THE INVENTION Embodiment 1

FIG. 1 is a diagram showing the constitution of a white organic ELdevice according to one embodiment of the invention. FIG. 2 is an energylevel diagram of a first emitting layer, an electron barrier layer and asecond emitting layer in this organic EL device.

As shown in FIG. 1, a white organic EL device 1 has a structure in whichan anode 2, a hole injecting layer 3, a hole transporting layer 4, afirst emitting layer 5, an electron barrier layer 6, a second emittinglayer 7, an electron-transporting layer 8 and a cathode 9 are stacked.The first emitting layer 5 contains a first host material and a firstdopant, and the second emitting layer 7 contains a second host materialand a second dopant.

In the device 1, white emission is obtained using the first emittinglayer 5 for blue emission and using the second emitting layer 7 for redemission.

FIG. 2 shows energy levels of the first emitting layer 5, electronbarrier layer 6 and second emitting layer 7 of the organic EL device 1.In this Figure, upper sides represent the affinity level of electrons,and lower sides represent ionization potential. In the energy leveldiagram, a lower portion exhibits a greater value.

The ionization potential of the electron barrier layer 6 is greater thanthat of the first emitting layer 5 by at least 0.1 eV, preferably by atleast 0.2 eV, more preferably by at least 0.3 eV. The affinity level ofthe electron barrier layer 6 is lower than those of the first emittinglayer 5 and the second emitting layer 7 by at least 0.1 eV, preferablyby at least 0.2 eV, more preferably at least 0.3 eV.

In FIG. 2, holes transported from the anode 2 (not shown) through thehole injecting layer 3 (not shown) and the hole transporting layer 4(not shown) are injected into the first emitting layer 5. Since,however, the electron barrier layer 6 constitutes a barrier, the holesare localized in a place X around the electron barrier layer 6. However,some holes move to the second emitting layer 7 through the electronbarrier layer 6. On the other hand, electrons transported from thecathode 9 (not shown) through the electron-transporting layer 8 (notshown) are injected into the second emitting layer 7. Since, however,the electron barrier layer 6 constitutes a barrier, the electrons arelocalized in a place Y around the electron barrier layer 6. However,some electrons move to the first emitting layer 5 through the electronbarrier layer 6. Therefore, the first emitting layer 5 and the secondemitting layer 7 emit light particularly in the places X and Y aroundthe electron barrier layer where holes or electrons are localized.

When the first emitting layer 5 is constituted from a material capableof transporting holes, holes injected from the hole transporting layer 4come to be easily transported to the place X in and in the vicinity ofthe electron barrier layer 6. When the second emitting layer 7 isconstituted from a material capable of transporting electrons, electronsinjected from the electron-transporting layer 8 come to be easilytransported to the place Y in and in the vicinity of the electronbarrier layer 6.

Preferably, the first emitting layer 5 has a hole mobility of at least10⁻⁵ cm²/v·s, and the second emitting layer 7 has an electron mobilityof at least 10⁻⁶ cm²/v·s. The hole or electron mobility is measured by a“time of flight” method.

In the white organic EL device 1 of this Embodiment, the electronbarrier layer 6 is present between the two emitting layers 5 and 7, andthe energy level of the electron barrier layer 6 is controlled wherebythe two emitting layers 5 and 7 hence emit light efficiently, so thathigh luminous efficiency can be realized. Since this white organic ELdevice has practical luminous efficiency, it can be suitably used in aninformation display, display equipment for automobile use, lightingfixtures, and the like.

In this Embodiment, the first emitting layer 5 is used for blueemission, and the second emitting layer 7 is used for red emission, butthey may be used in a reverse manner. The first host material and firstdopant of the first emitting layer 5 may be the same as, or differentfrom, the second host material and second dopant of the second emittinglayer 7, respectively, and they can be selected as required.

Further, the electron barrier layer 6 may contain a third dopant thatmay be the same as, or different from, the first and second dopants.When the electron barrier layer 6 contains a third dopant, there can berealized a device with a small change in chromaticity.

Preferably, the first, second and third dopants are selected from blue,green or red series that exhibit a yellow to orange or red color. Whenthey are selected in the above manner, the white chromaticity is easilyadjusted, and there can be realized a device with a small change inchromaticity.

In the invention, preferably, the emission maximum wavelength in blueemission is 450 to 500 nm, the emission maximum wavelength in greenemission is 500 to 550 nm, and the emission maximum wavelength in redemission is 550 to 650 nm.

Embodiment 2

FIG. 3 is a diagram showing the constitution of a white organic ELdevice according to another embodiment of the invention. FIG. 4 is anenergy level diagram of a first emitting layer, a first electron barrierlayer, a second electron barrier layer and a second emitting layer inthe organic EL device.

As shown in FIG. 3, this Embodiment is an embodiment in which theelectron barrier layer 6 of Embodiment 1 is replaced with a plurality ofelectron barrier layers 6 a and 6 b.

As shown in FIG. 4, the ionization potential of the electron barrierlayer 6 a is greater than that of the first emitting layer 5 by at least0.1 eV, preferably by at least 0.2 eV, and the affinity level of theelectron barrier layer 6 b is lower than that of the second emittinglayer 7 by at least 0.1 eV, preferably by at least 0.2 eV.

When such a plurality of electron barrier layers are provided, there canbe realized a device having higher luminous efficiency.

While this Embodiment has two electron barrier layers, three or moreelectron barrier layers may be provided. In this case, the electronbarrier layer nearest the anode constitutes a first electron barrierlayer, and the electron barrier layer nearest the cathode constitutes asecond electron barrier layer.

As described above, the invention has a constitution in which the anode,the first emitting layer, the electron barrier layer, the secondemitting layer and the cathode are stacked in this order. The electronbarrier layer may be formed of a plurality of layers. In the invention,another organic layer or inorganic layer may be interposed between theanode and the first emitting layer or between the second emitting layerand the cathode. The interposing layer is not limited so long as it cantransport electrons and holes. When the interposing layer is present inthe direction in which light is taken out, preferably, it istransparent. Examples of suitable organic EL devices of the inventioninclude the following constitutions.

-   -   Anode/first emitting layer/electron barrier layer/second        emitting layer/cathode,    -   Anode/hole transporting layer/first emitting layer/electron        barrier layer/second emitting layer/cathode,    -   Anode/first emitting layer/electron barrier layer/second        emitting layer/electron-transporting layer/cathode,    -   Anode/hole transporting layer/first emitting layer/electron        barrier layer/second emitting layer/electron-transporting        layer/cathode,    -   Anode/hole injecting layer/hole transporting layer/first        emitting layer/electron barrier layer/second emitting        layer/electron-transporting layer/cathode,    -   Anode/hole injecting layer/hole transporting layer/first        emitting layer/electron barrier layer/second emitting        layer/electron-transporting layer/electron-injecting        layer/cathode,    -   Anode/first emitting layer/first electron barrier layer/second        electron barrier layer/second emitting layer/cathode,    -   Anode/hole transporting layer/first emitting layer/first        electron barrier layer/second electron barrier layer/second        emitting layer/cathode,    -   Anode/first emitting layer/first electron barrier layer/second        electron barrier layer/second emitting        layer/electron-transporting layer/cathode,    -   Anode/hole transporting layer/first emitting layer/first        electron barrier layer/second electron barrier layer/second        emitting layer/electron-transporting layer/cathode,    -   Anode/hole injecting layer/hole transporting layer/first        emitting layer/first electron barrier layer/second electron        barrier layer/second emitting layer/electron-transporting        layer/cathode,    -   Anode/hole injecting layer/hole transporting layer/first        emitting layer/first electron barrier layer/second electron        barrier layer/second emitting layer/electron-transporting        layer/electron-injecting layer/cathode.

The invention will be explained below mainly with regard to the electronbarrier layer, blue emitting layer and red emitting layer which arecharacteristic portions of the invention. The red light as used hereinmeans light of a yellow color to an orange color or a red color. In theinvention, materials for the electron barrier layer and the emittinglayer are selected such that the electron barrier layer and the emittinglayer have certain energy levels. The constitutions and productionmethods of other organic layer, inorganic compound layer, anode,cathode, etc., will be briefly explained since general constitutions canbe employed therefor.

1. Electron Barrier Layer

The electron barrier layer is a layer for restricting the injection ofholes from an organic emitting layer near the anode to an organicemitting layer near the cathode and restricting the injection ofelectrons from an organic emitting layer near the cathode to an organicemitting layer near the anode, and the electron barrier layer isprovided for adjusting the emission quantity of each emitting layer.

When a single electron barrier layer is used, the material constitutingthe electron barrier layer has an ionization potential that is greaterthan the ionization potential of the organic emitting layer near theanode by at least 0.1 eV, and the electron barrier layer has an affinitylevel that is lower than the affinity level of any organic emittinglayer by at least 0.1 eV. The difference in the ionization potential orthe affinity level is preferably at least 0.2 eV.

Further, a plurality of electron barrier layers may be stacked. In thiscase, the electron barrier layer nearest the anode has an ionizationpotential that is greater than the ionization potential of the organicemitting layer near the anode by at least 0.1 eV, and the electronbarrier layer nearest the cathode has an affinity level that is lowerthan the affinity level of the organic layer near the cathode by atleast 0.1 eV. The difference in the ionization potential or the affinitylevel is preferably at least 0.2 eV.

Although not specially limited, the thickness of the electron barrierlayer is preferably 0.1 to 50 nm, more preferably 0.1 to 10 nm.

For the electron barrier layer, various organic compounds and inorganiccompounds can be used. The organic compounds include tertiary aminecompounds, carbazole derivatives, nitrogen-containing heterocycliccompounds and metal complexes. The inorganic compounds include oxides,nitrides, composite oxides, sulfides and fluorides of metals such as Ba,Ca, Sr, Yb, Al, Ga, In, Li, Na, K, Cd, Mg, Si, Ta, Ge, Sb, Zn, Cs, Eu,Y, Ce, W, Zr, La, Sc, Rb, Lu, Ti, Cr, Ho, Cu, Er, Sm, W, Co, Se, Hf, Tm,Fe and Nb.

The electron barrier layer may contain a blue, green or red dopant whichwill be explained below.

2. Emitting Layer

(1) Blue Emitting Layer

The blue emitting layer is preferably an emitting layer having anemission maximum wavelength of 450 to 500 nm, and comprises a hostmaterial and a blue dopant. The host material is preferably a styrylderivative, arylene derivative or aromatic amine. The styryl derivativeis particularly preferably at least one selected from distyrylderivatives, tristyryl derivatives, tetrastyryl derivatives andstyrylamine derivatives. The arylene derivative is particularlypreferably an anthracene derivative, especially a compound that containsarylanthracene skeleton. The aromatic amine is preferably a compoundcontaining 2 to 4 nitrogen atoms substituted with an aromatic group.Particularly preferred is a compound containing 2 to 4 nitrogen atomssubstituted with an aromatic group and at least one alkenyl group.

The styryl and anthracene derivatives include compounds represented bythe following formulas [1] to [6] and the aromatic amines includecompounds represented by the following formulas [7] to [8].

wherein R¹ to R⁸ are independently a hydrogen atom, a halogen atom, acyano group, a nitro group, a substituted or unsubstituted alkyl groupwith 1 to 20 carbon atoms, a substituted or unsubstituted alkoxy groupwith 1 to 20 carbon atoms, a substituted or unsubstituted aryloxy groupwith 6 to 30 carbon atoms, a substituted or unsubstituted alkylthiogroup with 1 to 20 carbon atoms, a substituted or unsubstituted arylthiogroup with 6 to 30 carbon atoms, a substituted or unsubstitutedarylalkyl group with 7 to 30 carbon atoms, a substituted orunsubstituted monocyclic group with 5 to 30 carbon atoms, a substitutedor unsubstituted condensed polycyclic group with 10 to 30 carbon atomsor a substituted or unsubstituted hetrocyclic group with 5 to 30 carbonatoms; and Ar¹ and Ar² are independently a substituted or unsubstitutedaryl group with 6 to 30 carbon atoms or a substituted or unsubstitutedalkenyl group, a substituent is a substituted or unsubstituted alkylgroup with 1 to 20 carbon atoms, a substituted or unsubstituted alkoxygroup with 1 to 20 carbon atoms, a substituted or unsubstituted aryloxygroup with 6 to 30 carbon atoms, a substituted or unsubstitutedalkylthio group with 1 to 20 carbon atoms, a substituted orunsubstituted arylthio group with 6 to 30 carbon atoms, a substituted orunsubstituted arylalkyl group with 6 to 30 carbon atoms, a substitutedor unsubstituted monocyclic group with 5 to 30 carbon atoms, asubstituted or unsubstituted condensed polycyclic group with 10 to 30carbon atoms, a substituted or unsubstituted hetrocyclic group with 5 to30 carbon atoms or a substituted or unsubstituted alkenyl group with 4to 40 carbon atoms.

wherein R¹ to R¹⁰ and Ar¹ and Ar² are the same as those in the formula[1].

wherein R¹ to R¹⁰ and Ar³ and Ar⁴ are the same as those in the formula[1], 1 is 1 to 3, m is 1 to 3 and l+m is 2 or more.

wherein R¹ to R⁸ and Ar¹ and Ar² are the same as those in the formula[1].

wherein R¹¹ to R²⁰ are independently a hydrogen atom, an alkenyl group,an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, anaryloxy group, an alkylamino group, an arylamino group or a substitutedor unsubstituted heterocyclic group; a and b are each an integer of 1 to5; when they are 2 or more, R¹¹s or R¹²s may be the same or different,or R¹¹s or R¹²s may be bonded together to form a ring; R¹³ and R¹⁴, R¹⁵and R¹⁶, R¹⁷ and R¹⁸, or R¹⁹ and R²⁰ may be bonded together to form aring; and L¹ is a single bond, —O—, —S—, —N(R)— (R is an alkyl group ora substituted or unsubstituted aryl group) or an arylene group.

wherein R²¹ to R³⁰ are independently a hydrogen atom, an alkenyl group,an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, anaryloxy group, an alkylamino group, an arylamino group or a substitutedor unsubstituted heterocyclic group; c, d, e and f are each an integerof 1 to 5; when they are 2 or more, R²¹s, R²²s, R²⁶s or R²⁷s may be thesame or different, R²¹s, R²²s, R²⁶s or R²⁷s may be bonded together toform a ring, or R²³ and R²⁴, or R²⁸ and R²⁹ may be bonded together toform a ring; and L² is a single bond, —O—, —S—, —N(R)— (R is an alkylgroup or a substituted or unsubstituted aryl group) or an arylene group.

wherein Ar⁵, Ar⁶ and Ar⁷ are independently a substituted orunsubstituted monovalent aromatic group with 6 to 40 carbon atoms, atleast one of them may include a styryl group and g is an integer of 1 to4.

wherein Ar⁸, Ar⁹, Ar¹¹, Ar¹³ and Ar¹⁴ are independently a substituted orunsubstituted monovalent aromatic group with 6 to 40 carbon atoms, Ar¹⁰and Ar¹² are independently a substituted or unsubstituted divalentaromatic group with 6 to 40 carbon atoms, at least one of Ar⁸ to Ar¹⁴may include a styryl group or styrylene group, h and k are each aninteger of 0 to 2 and i and j are each an integer of 0 to 3.

A blue dopant is preferably at least one selected from styrylamines,amine-substituted styryl compounds and compounds containing fusedaromatic rings. A blue dopant may comprise multiple kinds of compounds.Examples of the above-mentioned styryl amines and amine-substitutedstyryl compounds include compounds represented by the general formulas[9] to [10] and examples of the above-mentioned compounds containingfused aromatic rings are compounds represented by the general formula[11].

wherein Ar⁵, Ar⁶, and Ar⁷ are independently a substituted orunsubstituted aromatic group with 6 to 40 carbon atoms; at least one ofthem includes a styryl group and p is an integer of 1 to 3.

wherein Ar¹⁵ and Ar¹⁶ are independently an arylene group with 6 to 30carbon atoms; E¹ and E² are independently an aryl or alkyl group with 6to 30 carbon atoms, a hydrogen atom, or a cyano group; q is an integerof 1 to 3; U and/or V are a substituent including an amino group and theamino group is preferably an arylamino group.

wherein A is an alkyl group or an alkoxy group with 1 to 16 carbonatoms, a substituted or unsubstituted aryl group with 6 to 30 carbonatoms, a substituted or unsubstituted alkylamino group with 6 to 30carbon atoms, a substituted or unsubstituted arylamino group with 6 to30 carbon atoms and B is a fused aromatic ring group with 10 to 40carbon atoms; and r is an integer of 1 to 4.

As a blue emitting layer, an emitting layer containing a phosphorescentcompound can be used. A host material is preferably a compoundcontaining a carbazole ring. Specific examples are shown below.

Examples of the host compounds other than the compounds shown aboveinclude triazole, oxazole, oxadiazole, imidazole, polyarylalkane,pyrazoline, pyrazolone, phenylanediamine, arylamine, amino-substitutedcalcone, styryl anthracene, fluorenone, hydrazone, stilbene and silazanederivatives; aromatic tertiary amine, styrylamine, aromaticdimethylidene and porphyrin compounds; anthraquinodimethane, anthrone,diphenylquinone, thiopyrandioxide, carbodiimide, fluoreniridenemethaneand distyrylpyrazine derivatives; hetrocyclic tetracarboxylic anhydridessuch as naphthaleneperylene; phthalocyanine derivatives; metal complexesof 8-quinolinol derivatives, various metal complex polysilane compoundsrepresented by metal complexes having metalphthalocyanine, benzoxazoleor benzothiaole as a ligand; electroconductive high molecular oligomerssuch as poly(N-vinylcarbazole) derivatives, aniline copolymers,thiophene oligomers and polythiophene; and polymer compounds such aspolythiophene, polyphenylene, polyphenylenevinylene and polyfluorenederivatives. Host compounds can be used individually or as a combinationof two or more kinds.

A phosphorescent dopant is a compound that can emit light from tripletexcitons. The dopant is not limited as long as it can emit light fromtriplet excitons, but it is preferably a metal complex containing atleast one metal selected from the group of Ir, Ru, Pd, Pt, Os and Re. Ofthese, a porphyrin metal complex or an ortho-metalated metal complex ispreferable. As a porphyrin metal complex, a porphyrin platinum complexis preferable. There are various ligands forming an ortho-metalatedmetal complex. Preferable ligands include 2-phenylpyridine,7,8-benzoquinoline, 2-(2-thienyl)pyridine, 2-(1-naphtyl)pyridine and2-phenylquinoline derivatives. These derivatives can containsubstituents if necessary. Fluorides and derivatives containing atrifluoromethyl group are particularly preferable as a blue dopant. Asan auxiliary ligand, ligands other than acetylacetonate and picric acidmay be contained. The phosphorescent dopants can be used individually oras a combination of two or more kinds.

The content of a phosphorescent dopant in a blue emitting layer is notlimited and can be properly selected according to purposes; for example,it is 0.1 to 70 mass %, preferably 1 to 30 mass %. When the content of aphosphorescent dopant is less than 0.1 mass %, the sufficient effect bythe addition thereof may be brought about. When the content exceeds 70mass %, the device performance may be degraded due to the phenomenoncalled concentration quenching.

The thickness of a blue emitting layer is preferably 5 to 30 nm, morepreferably 7 to 30 nm and most preferably 10 to 30 nm. When it is lessthan 5 nm, the formation of an emitting layer and the adjustment ofchromaticity may become difficult. When it exceeds 30 nm, the drivingvoltage may increase.

(2) Red (Yellow-to-Orange or Yellow-to-Red) Emitting Layer

The red emitting layer is preferably an emitting layer which emits lightwith a maximum wavelength of 550 to 650 nm; and made of a host materialand a yellow-to-orange or yellow-to-red dopant. Examples of the hostmaterial are preferably styryl derivatives, anthracene derivatives,aromatic amines, and metal complexes of 8-hydroxyquinoline or itsderivatives. As examples of the styryl derivatives, anthracenederivatives and aromatic amines, host materials used for a blue emittinglayer can also be used for a yellow-to-orange or yellow-to-red emittinglayer. As examples of the metal complexes of 8-hydroxyquinoline or itsderivatives, metal chelate oxynoide compounds including chelates ofoxine (generally 8-quinolinol or 8-hydroxyquinoline), such astris(8-quinolinol)aluminum, can be used. When a compound with a highelectron-transporting property such as anthracene derivatives is used asa host material, host materials for a blue emitting layer and ayellow-to-orange or yellow-to-red emitting layer may be the same ordifferent.

There can be used as a yellow-to-orange or a yellow-to-red dopantflorescent compound containing at least one of a fluoranthene skeletonand a perylene skeleton. Examples include compounds represented by thefollowing general formulas [12] to [28].

wherein X¹ to X²⁰ are independently a hydrogen atom, a linear, branchedor cyclic alkyl group with 1 to 20 carbon atoms, a linear, branched orcyclic alkoxy group with 1 to 20 carbon atoms, a substituted orunsubstituted aryl group with 6 to 30 carbon atoms, a substituted orunsubstituted aryloxy group with 6 to 30 carbon atoms, a substituted orunsubstituted arylamino group with 6 to 30 carbon atoms, a substitutedor unsubstituted alkylamino group with 1 to 30 carbon atoms, asubstituted or unsubstituted arylalkylamino group with 7 to 30 carbonatoms or a substituted or unsubstituted alkenyl group with 8 to 30carbon atoms; adjacent substituents and X¹ to X²⁰ may be bonded togetherto form a ring structure; and when adjacent substituents are an arylgroup, the substituents may be the same.

The compounds represented by the general formulas [12] to [26]preferably contain an amino group or an alkenyl group.

wherein X²¹ to X²⁴ are independently an alkyl group with 1 to 20 carbonatoms, a substituted or unsubstituted aryl group with 6 to 30 carbonatoms; X²¹ and X²² and/or X²³ and X²⁴ may be bonded to each other with acarbon to carbon bond, —O— or —S— therebetween; X²⁵ to X³⁶ areindependently a hydrogen atom, a linear, branched or cyclic alkyl groupwith 1 to 20 carbon atoms, a linear, branched or cyclic alkoxy groupwith 1 to 20 carbon atoms, a substituted or unsubstituted aryl groupwith 6 to 30 carbon atoms, a substituted or unsubstituted aryloxy groupwith 6 to 30 carbon atoms, a substituted or unsubstituted arylaminogroup with 6 to 30 carbon atoms, a substituted or unsubstitutedalkylamino group with 1 to 30 carbon atoms, a substituted orunsubstituted arylalkylamino group with 7 to 30 carbon atoms or asubstituted or unsubstituted alkenyl group with 8 to 30 carbon atoms;adjacent substituents and X²⁵ to X³⁶ may be bonded together to form aring structure; and at least one of the substituents X²⁵ to X³⁶ in eachof the formulas preferably contain an amino or alkenyl group.

A florescent compound containing a fluoranthene skeleton preferablycontains an electron-donating group for high performance and longlifetime. A preferable electron-donating group is a substituted orunsubstituted arylamino group. A fluorescent compound containing afluoranthene skeleton preferably has 5 or more fused rings, morepreferably 6 or more fused rings, for the following reason. Thefluorescent compound has a fluorescent peak wavelength of 540 to 700 nm.The emission from a blue emitting material and emission from thefluorescent compound overlap to give a white color. The above-mentionedfluorescent compound preferably contains a plurality of fluorantheneskeletons since the emitted light color falls in the yellow-to-orange oryellow-to-red zone. Particularly preferred fluorescent compound containsan electron-donating group and a fluoranthene or perylene skeleton andhas a fluorescent peak wavelength of 540 to 700 nm.

As a red emitting layer, an emitting layer to which a phosphorescentemitting dopant is added can be used. A host material in such a case ispreferably a compound containing a carbazole ring and the compounds usedfor a blue emitting layer can be used.

A phosphorescent dopant is a compound that can emit from tripletexcitons and is not limited as long as it can emit from triplet excitonsbut it is preferably a metal complex containing at least one metalselected from the group of Ir, Ru, Pd, Pt, Os and Re. Of these, aporphyrin metal complex or an ortho-metalated metal complex ispreferable. There are various ligands forming an ortho-metalated metalcomplex. Preferable ligands include 2-phenylpyridine, 7,8-benoquinoline,2-(1-naphtyl)pyridine and 2-phenylquinoline derivatives. Thesederivatives can contain substituents if necessary. Preferred are2-phenylquinoline derivatives, 2-(2-thienyl)pyridine derivatives and thelike as a yellow-to-red dopant. Ligands other than the above-mentionedligands, such as acetylacetonate and picric acid, may be contained as anauxiliary ligand.

The content of a phosphorescent dopant in a red emitting layer can beproperly selected according to purposes; it is preferably 0.1 to 70 mass%, more preferably 1 to 30 mass %. When the content of a phosphorescentcompound is less than 0.1 mass %, insufficient effect may be broughtabout. When the content exceeds 70 mass %, the phenomenon calledconcentration quenching may significantly proceed, thereby degrading thedevice performance.

The thickness of a red emitting layer is preferably 10 to 50 nm, morepreferably 20 to 50 nm and most preferably 30 to 50 nm. When it is lessthan 10 nm, the luminous efficiency may decrease. When it exceeds 50 nm,the driving voltage may increase.

(2) Green Emitting Layer

The green emitting layer is preferably a layer which emits light with amaximum wavelength of 500 to 550 nm; and made of a host material and agreen dopant. The host material are preferably styryl derivatives,anthracene derivatives, aromatic amines, and metal complexes of8-hydroxyquinoline or its derivatives. As specific examples of thestyryl derivatives, anthracene derivatives and aromatic amines, hostmaterials used for a blue emitting layer can also be used for a greenemitting layer. As specific examples of the metal complexes of8-hydroxyquinoline or its derivatives, metal chelate oxynoide compoundsincluding chelates of oxine (generally 8-quinolinol or8-hydroxyquinoline), for example, tris(8-quinolinol)aluminum, can beused. When a compound with an electron-transporting property such asanthracene derivatives is used as a host material, host materials for ablue emitting layer and a green emitting layer may be the same ordifferent. Examples of the green dopants include C545T[10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,2,7,7-tetramethyl-1H, 5H,11H-[1]benzopyrano[6,7,8-ij]quinolizine-1′-one].

There can be used as a green dopant an emitting layer containing aphosphorescent compound. A host material in such a case is preferably acompound containing a carbazole ring and the compound used for a blueemitting layer can be used.

A phosphorescent dopant is a compound that can emit from tripletexcitons and is not limited as long as it can emit from triplet excitonsbut it is preferably a metal complex containing at least one metalselected from the group of Ir, Ru, Pd, Pt, Os and Re. Of these, aporphyrin metal complex or an ortho-metalated metal complex ispreferable. As the porphyrin metal complex, porphyrin platinum complexis preferable. There are various ligands forming an ortho-metalatedmetal complex. Preferable ligands include 2-phenylpyridine,7,8-benoquinoline, 2-(2-thienyl)pyridine, 2-(1-naphtyl)pyridine and2-phenylquinoline derivatives. These derivatives can containsubstituents if necessary. Particularly preferred are 2-phenylquinolinederivatives, as a green dopant. Ligands other than the above-mentionedligands may be contained as an auxiliary ligand. The phosphorescentdopants may be used individually or as a combination of two or morekinds.

The content of a phosphorescent dopant in a green emitting layer is notlimited and can be properly selected according to purposes; but it ispreferably 0.1 to 70 mass %, more preferably 1 to 30 mass %. When thecontent of a phosphorescent compound is less than 0.1 mass %,insufficient effect may be brought about. When the content exceeds 70mass %, due to the phenomenon called concentration quenching the deviceperformance may be degraded.

The thickness of a green emitting layer is preferably 10 to 50 nm, morepreferably 20 to 50 nm and most preferably 30 to 50 nm. When it is lessthan 10 nm, the luminous efficiency may decrease. When it exceeds 50 nm,the driving voltage may increase.

2. Other Organic Layers

(1) First Organic Layer

A hole-injecting layer, a hole-transporting layer, an organicsemiconductor layer and the like can be arranged between the anode andthe emitting layer as a first organic layer. The hole-injecting layer orthe hole-transporting layer is a layer for helping the injection ofholes into the emitting layer so as to transport holes to an emittingregion. The hole mobility thereof is large and the ionization energythereof is usually as small as 5.5 eV or less. A hole-injecting layer isformed to control energy level, for example, to reduce rapid energylevel changes. Such a hole-injecting or hole-transporting layer ispreferably made of a material which can transport holes to the emittinglayer at a low electric field intensity. The hole mobility thereof ispreferably at least 10⁻⁶ cm²/V·second when an electric field of, e.g.,10⁴ to 10⁶ V/cm is applied. The material for forming the hole-injectinglayer or the hole-transporting layer can be arbitrarily selected frommaterials which have been widely used as a material transportingelectric charge of holes in photoconductive materials and knownmaterials used in a hole-injecting layer of organic EL devices.

Specific examples of materials for a hole-injecting layer and ahole-transporting layer, include triazole derivatives (see U.S. Pat. No.3,112,197 and others), oxadiazole derivatives (see U.S. Pat. No.3,189,447 and others), imidazole derivatives (see JP-B-37-16096 andothers), polyarylalkane derivatives (see U.S. Pat. Nos. 3,615,402,3,820,989 and 3,542,544, JP-B-45-555 and 51-10983, JP-A-51-93224,55-17105, 56-4148, 55-108667, 55-156953 and 56-36656, and others),pyrazoline derivatives and pyrazolone derivatives (see U.S. Pat. Nos.3,180,729 and 4,278,746, JP-A-55-88064, 55-88065, 49-105537, 55-51086,56-80051, 56-88141, 57-45545, 54-112637 and 55-74546, and others),phenylene diamine derivatives (see U.S. Pat. No. 3,615,404,JP-B-51-10105, 46-3712 and 47-25336, JP-A-54-53435, 54-110536 and54-119925, and others), arylamine derivatives (see U.S. Pat. Nos.3,567,450, 3,180,703, 3,240,597, 3,658,520, 4,232,103, 4,175,961 and4,012,376, JP-B-49-35702 and 39-27577, JP-A-55-144250, 56-119132 and56-22437, DE1,110,518, and others), amino-substituted chalconederivatives (see U.S. Pat. No. 3,526,501, and others), oxazolederivatives (ones disclosed in U.S. Pat. No. 3,257,203, and others),styrylanthracene derivatives (see JP-A-56-46234, and others), fluorenonederivatives (JP-A-54-110837, and others), hydrazone derivatives (seeU.S. Pat. No. 3,717,462, JP-A-54-59143, 55-52063, 55-52064, 55-46760,55-85495, 57-11350, 57-148749 and 2-311591, and others), stilbenederivatives (see JP-A-61-210363, 61-228451, 61-14642, 61-72255,62-47646, 62-36674, 62-10652, 62-30255, 60-93455, 60-94462, 60-174749and 60-175052, and others), silazane derivatives (U.S. Pat. No.4,950,950), polysilanes (JP-A-2-204996), aniline copolymers(JP-A-2-282263), and electroconductive high molecular oligomers (inparticular thiophene oligomers) disclosed in JP-A-1-211399.

The above-mentioned substances can be used as the material of thehole-injecting layer or the hole-transporting layer. The following canalso be used: porphyrin compounds (disclosed in JP-A-63-2956965 andothers), aromatic tertiary amine compounds and styrylamine compounds(see U.S. Pat. No. 4,127,412, JP-A-53-27033, 54-58445, 54-149634,54-64299, 55-79450, 55-144250, 56-119132, 61-295558, 61-98353 and63-295695, and others), and aromatic tertiary amine compounds. Thefollowing can also be given as examples:4,4′-bis(N-(1-naphthyl)-N-phenylamino)biphenyl, which has in themolecule thereof two condensed aromatic rings, disclosed in U.S. Pat.No. 5,061,569, and 4,4′, 4″-tris(N-(3-methylphenyl)-N-phenylamino)triphenylamine, wherein three triphenylamine units are linked to eachother in a star-burst form, disclosed in JP-A-4-308688. Inorganiccompounds such as aromatic dimethylidene type compounds, mentioned aboveas the material for an emitting layer, and p-type Si and p-type SiC canalso be used as the material of the hole-injecting layer or thehole-transporting layer.

This hole-injecting layer or the hole-transporting layer may be a singlelayer made of one or more of the above-mentioned materials.Hole-injecting layers or the hole-transporting layers made of compoundsdifferent from each other may be stacked. The thickness of thehole-injecting layer or the hole-transporting layer is not particularlylimited, and is preferably 20 to 200 nm.

The organic semiconductor layer is a layer for helping the injection ofholes or electrons into the emitting layer, and is preferably a layerhaving an electroconductivity of 10⁻¹⁰ S/cm or more. The material ofsuch an organic semiconductor layer may be an electroconductiveoligomer, such as thiophene-containing oligomers or arylamine-containingoligomers disclosed in JP-A-8-193191, electroconductive dendrimers suchas arylamine-containing dendrimers. The thickness of the organicsemiconductor layer is not particularly limited, and is preferably 10 to1,000 nm.

(2) Second Organic Layer

An electron-injecting layer, an electron-transporting layer and the likecan be arranged between a cathode and an emitting layer as a secondorganic layer. The electron-injecting layer or the electron-transportinglayer is a layer for helping the injection of electrons into theemitting layer, and has a large electron mobility. Theelectron-injecting layer is formed to control energy level, for example,to reduce rapid energy level changes.

The thickness of electron-transporting layer is properly selectedseveral nm to several μm but preferably selected such that the electronmobility is 10⁻⁵ cm²/Vs or more when applied with an electric field of10⁴ to 10⁶ V/cm.

The material used for the electron-injecting layer is preferably a metalcomplex of 8-hydroxyquinoline or a derivative thereof.

Specific examples of the metal complex of 8-hydroxyquinoline or aderivative thereof include metal chelate oxynoid compounds containing achelate of oxine (generally, 8-quinolinol or 8-hydroxyquinoline).

For example, Alq described in the explanation of the emitting materialcan be used for the electron-injecting layer.

Examples of the oxadiazole derivatives include electron-transportingcompounds represented by the following general formulas:

wherein Ar¹⁷, Ar¹⁸, Ar¹⁹, Ar²¹, Ar²² and Ar²⁵ may be the same ordifferent and each represent a substituted or unsubstituted aryl group;and Ar²⁰, Ar²³ and Ar²⁴ may be the same or different and each representa substituted or unsubstituted arylene group.

Examples of the aryl group include phenyl, biphenyl, anthranyl,perylenyl, and pyrenyl groups. Examples of the arylene group includephenylene, naphthylene, biphenylene, anthranylene, perylenylene, andpyrenylene groups. Examples of the substituents include alkyl groupswith 1 to 10 carbon atoms, alkoxy groups with 1 to 10 carbon atoms, anda cyano group. The electron-transporting compounds are preferably onesfrom which a thin film can be easily formed.

Specific examples of the electron-transporting compounds are mentionedbelow.

In the formulas, tBu represents a tert-butyl group and Me represents amethyl group.Nitrogen-containing heterocyclic compounds represented by the followingformulas

wherein A¹ to A³ is a nitrogen atom or carbon atom;

R is a substituted or unsubstituted aryl group with 6 to 60 carbonatoms, a substituted or unsubstituted heteroaryl group with 3 to 60carbon atoms, an alkyl group with 1 to 20 carbon atoms, a haloalkylgroup with 1 to 20 carbon atoms, or an alkoxy group with 1 to 20 carbonatoms; n is an integer of 0 to 5 and when n is an integer of 2 or more,Rs may be the same or different or adjacent Rs may be bonded to eachother to form a substituted or unsubstituted carbocyclic aliphatic ringor a substituted or unsubstituted carbocyclic aromatic ring;

Ar²⁶ is a substituted or unsubstituted aryl group with 6 to 60 carbonatoms, or a substituted or unsubstituted heteroaryl group with 3 to 60carbon atoms;

Ar²⁷ is a hydrogen atom, an alkyl group with 1 to 20 carbon atoms, ahaloalkyl group with 1 to 20 carbon atoms, an alkoxy group with 1 to 20carbon atoms, a substituted or unsubstituted aryl group with 6 to 60carbon atoms, or a substituted or unsubstituted heteroaryl group with 3to 60 carbon atoms;

Ar^(26′) is a substituted or unsubstituted arylene group with 6 to 60carbon atoms, or a substituted or unsubstituted heteroarylene group with3 to 60 carbon atoms;

provided that either one of Ar²⁶, Ar²⁷ and Ar^(26′) is a substituted orunsubstituted condensed cyclic group with 10 to 60 carbon atoms or asubstituted or unsubstituted condensed heterocyclic group with 3 to 60carbon atoms;

L³ and L⁴ are each a single bond, a substituted or unsubstitutedcondensed cyclic group with 6 to 60 carbon atoms, a substituted orunsubstituted condensed heterocyclic group with 3 to 60 carbon atoms, ora substituted or unsubstituted fluorenylene group.

Nitrogen-containing heterocyclic compounds represented by the followingformula:

HAr-L⁵-Ar²⁸—Ar²⁹

wherein HAr is a substituted or unsubstituted nitrogen-containingheterocyclic ring with 3 to 40 carbon atoms;

L⁵ is a single bond, a substituted or unsubstituted arylene group with 6to 60 carbon atoms, a substituted or unsubstituted heteroarylene groupwith 3 to 60 carbon atoms, or a substituted or unsubstitutedfluorenylene group;

Ar²⁸ is a substituted or unsubstituted bivalent aromatic hydrocarbongroup with 6 to 60 carbon atoms;

Ar²⁹ is a substituted or unsubstituted aryl group with 6 to 60 carbonatoms or a substituted or unsubstituted heteroaryl group with 3 to 60carbon atoms.

An EL device using a silacyclopentadiene derivative represented by thefollowing formula, disclosed in JP-A-09-087616:

wherein Q¹ and Q² are each a saturated or unsaturated hydrocarbon groupwith 1 to 6 carbon atoms, an alkoxy group, an alkenyloxy group, analkynyloxy group, a hydroxyl group, a substituted or unsubstituted arylgroup, or a substituted or unsubstituted heterocyclic group, or Q¹ or Q²are bonded to each other to form a saturated or unsaturated ring; R³¹ toR³⁴ are each a hydrogen atom, a halogen atom, a substituted orunsubstituted alkyl group with 1 to 6 carbon atoms, an alkoxy group, anaryloxy group, a perfluoroalkyl group, a perfluoroalkoxy group, an aminogroup, an alkylcarbonyl group, an arylcarbonyl group, an alkoxycarbonylgroup, an aryloxycarbonyl group, an azo group, an alkylcarbonyloxygroup, an arylcarbonyloxy group, an alkoxycarbonyloxy group, anaryloxycarbonyloxy group, a sulfinyl group, a sulfonyl group, a sulfanylgroup, a silyl group, a carbamoil group, an aryl group, a heterocyclicgroup, an alkenyl group, an alkynyl group, a nitro group, a formylgroup, a nitroso group, a formyloxy group, an isocyano group, a cyanategroup, an isocyanate group, a thiocyanate group, an isothiocyanate groupor a cyano group, or adjacent R³¹ to R³⁴ may form a substituted orunsubstituted condensed ring structure.Silacyclopentadiene derivatives represented by the following formula,disclosed in JP-A-09-194487:

wherein Q³ and Q⁴ are each a saturated or unsaturated hydrocarbon groupwith 1 to 6 carbon atoms, an alkoxy group, an alkenyloxy group, analkynyloxy group, a substituted or unsubstituted aryl group, or asubstituted or unsubstituted heterocyclic group, or Q³ or Q⁴ are bondedto each other to form a saturated or unsaturated ring; R³⁵ to R³⁸ areeach a hydrogen atom, a halogen atom, a substituted or unsubstitutedalkyl group with 1 to 6 carbon atoms, an alkoxy group, an aryloxy group,a perfluoroalkyl group, a perfluoroalkoxy group, an amino group, analkylcarbonyl group, an arylcarbonyl group, an alkoxycarbonyl group, anaryloxycarbonyl group, an azo group, an alkylcarbonyloxy group, anarylcarbonyloxy group, an alkoxycarbonyloxy group, an aryloxycarbonyloxygroup, a sulfinyl group, a sulfonyl group, a sulfanyl group, a silylgroup, a carbamoil group, an aryl group, a heterocyclic group, analkenyl group, an alkynyl group, a nitro group, a formyl group, anitroso group, a formyloxy group, an isocyano group, a cyanate group, anisocyanate group, a thiocyanate group, an isothiocyanate group or acyano group, or adjacent R³⁵ to R³⁸ may bond to form a structure whereinsubstituted or unsubstituted rings are condensed to each other;

provided that in the case where R³⁵ and R³⁸ are phenyl groups, Q³ and Q⁴are neither alkyl groups nor phenyl groups; in the case where R³⁵ andR³⁸ are thienyl groups, Q³, Q⁴, R³⁶ and R³⁷ do not form the structuresatisfying the conditions at the same time that where Q³ and Q⁴ aremonovalent hydrocarbon groups, and R³⁶ and R³⁷ are each an alkyl group,an aryl group, an alkenyl, or an aliphatic ring group formed by R³⁶ andR³⁷ bonded to each other; in the case where R³⁵ and R³⁸ are silylgroups, R³⁶, R³⁷, Q³ and Q⁴ are each neither a monovalent hydrocarbongroup with 1 to 6 carbon atoms nor a hydrogen atom; and in the casewhere R³⁵ and R³⁶ form a condensed structure with benzene rings, Q³ andQ⁴ are neither an alkyl group nor a phenyl group.

Borane derivatives represented by the following formula, disclosed inJP-A1-2000-040586:

wherein R³⁹ to R⁴⁶ and Q⁸ are each a hydrogen atom, a saturated orunsaturated hydrocarbon group, an aromatic group, a heterocyclic group,a substituted amino group, a substituted boryl group, an alkoxy group oran aryloxy group; Q⁵, Q⁶ and Q⁷ are each a saturated or unsaturatedhydrocarbon group, an aromatic group, a heterocyclic group, asubstituted amino group, an alkoxy group or an aryloxy group; thesubstituents of Q⁷ and Q⁸ may be bonded to each other to form acondensed ring; s is an integer of 1 to 3, and Q⁷s may be different fromeach other when s is 2 or more; provided that excluded are the compoundswhere s is 1, Q⁵, Q⁶ and R⁴⁰ are methyl groups and R⁴⁶ is a hydrogenatom or substituted boryl group, and the compounds where s is 3 and Q⁷is a methyl group.Compounds represented by the following formula, disclosed inJP-A-10-088121:

wherein Q⁹ and Q″ are independently a ligand represented by thefollowing formula (3); and L⁶ is a ligand represented by a halogen atom,a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted arylgroup, a substituted or unsubstituted heterocyclic group, —OR⁴⁷ (R⁴⁷ isa hydrogen atom, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted cycloalkyl group, a substituted orunsubstituted aryl group, a substituted or unsubstituted heterocyclicgroup), or —O—Ga-Q¹¹ (Q¹²) (Q¹¹ and Q¹² represent the same meanings asQ⁹ and Q¹⁰.

wherein rings A⁴ and A⁵ are each a substituted or unsubstituted6-membered aryl rings which are condensed to each other.

The metal complexes have the strong nature of an n-type semiconductorand large ability of injecting electrons. Further the energy generatedat the time of forming such a complex is small and therefore strongbonding can be obtained between a metal and ligands in the complexformed, and a fluorescent quantum efficiency is large.

Specific examples of the rings A⁴ and A⁵ which form the ligands of theabove formula include halogen atoms such as chlorine, bromine, iodineand fluorine; substituted or unsubstituted alkyl groups such as methyl,ethyl, propyl, butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl,octyl, stearyl and trichloromethyl; substituted or unsubstituted arylgroups such as phenyl, naphthyl, 3-methylphenyl, 3-methoxyphenyl,3-fluorophenyl, 3-trichloromethylphenyl, 3-trifluoromethylphenyl and3-nitrophenyl; substituted or unsubstituted alkoxy groups such asmethoxy, n-butoxy, tert-butoxy, trichloromethoxy, trifluoroethoxy,pentafluoropropoxy, 2,2,3,3-tetrafluoropropoxy,1,1,1,3,3,3-hexafluoro-2-propoxy and 6-(perfluoroethyl)hexyloxy;substituted or unsubstituted aryloxy groups such as phenoxy,p-nitrophenoxy, p-tert-butylphenoxy, 3-fluorophenoxy, pentafluorophenoxyand 3-trifluoromethylphenoxy; substituted or unsubstituted alkylthiogroups such as methylhio, ethylthio, tert-butylthio, hexylthio,octylthio and trifruoromethyltio; substituted or unsubstituted arylthiogroups such as phenylthio, p-nitrophenylthio, p-tert-butylphenylthio,3-fluorophenylthio, pentafluorophenylthio and3-trifluoromethylphenylthio; a cyano group; a nitro group, an aminogroup; mono or di-substituted amino groups such as methylamino,dimethylamino, ethylamino, diethylamino, dipropylamino, dibutylamino anddiphenylamino; acylamino groups such as bis(acetoxymethyl)amino,bis(acetoxyethyl)amino, bis(acetoxypropyl)amino andbis(acetoxybutyl)amino; a hydroxy group; a siloxy group; an acyl group;a carbamoyl group; substituted carbamoyl groups such as methylcarbamoyl,dimethylcarbamoyl, ethylcarbamoyl, diethylcarbamoyl, propylcarbamoyl,butylcarbamoyl and phenylcarbamoyl; a carboxylic group; a sulfonic acidgroup; an imido group; cycloalkyl groups such as cyclopentyl andcyclohexyl; aryl groups such as phenyl, naphthyl, biphenyl, anthranyl,phenanthryl, fluorenyl and pyrenyl; and heterocyclic groups such aspyridinyl, pyrazinyl, pyrimidinyl, pryidazinyl, triazinyl, indolinyl,quinolinyl, acridinyl, pyrrolidinyl, dioxanyl, piperidinyl,morpholidinyl, piperazinyl, triathinyl, carbazolyl, furanyl, thiophenyl,oxazolyl, oxadiazolyl, benzooxazolyl, thiazolyl, thiadiazolyl,benzothiazolyl, triazolyl, imidazolyl, benzoimidazolyl and puranyl.Moreover the above-mentioned substituents may be bonded to each other toform a six-membered aryl or heterocyclic ring.

A reducing dopant may be contained in the electron-transporting regionor in an interfacial region between the cathode and the organic layer.The reducing dopant is defined as a substance which can reduce anelectron-transporting compound. Accordingly, various substances whichhave given reducing properties can be used. For example, at least onesubstance can be preferably used which is selected from the groupconsisting of alkali metals, alkaline earth metals, rare earth metals,alkali metal oxides, alkali metal halides, alkaline earth metal oxides,alkaline earth metal halides, rare earth metal oxides, rare earth metalhalides, alkali metal organic complexes, alkaline earth metal organiccomplexes, and rare earth metal organic complexes.

Specific examples of preferred reducing dopants include at least onealkali metal selected from the group consisting of Na (work function:2.36 eV), K (work function: 2.28 eV), Rb (work function: 2.16 eV) and Cs(work function: 1.95 eV) or at least one alkaline earth metal selectedfrom the group consisting of Ca (work function: 2.9 eV), Sr (workfunction: 2.0 to 2.5 eV) and Ba (work function: 2.52 eV). Particularlypreferred are ones having a work function of 2.9 eV or less. Amongthese, a more preferable reducing dopant is at least one alkali metalselected from the group consisting of K, Rb and Cs, even more preferablyRb and Cs and the most preferably Cs. These alkali metals have aparticularly high reducing ability, and therefore adding a relativelysmall amount thereof into an electron-injecting region enhances theluminance and lifetime of the organic EL device. As a reducing dopanthaving a work function of 2.9 eV or less, combinations of two or more ofthese alkali metals are preferable. Combinations with Cs, for example,Cs and Na, Cs and K, Cs and Rb or Cs, Na and K are particularlypreferable. The combination with Cs efficiently exhibits a reducingability and the addition thereof into an electron-injecting regionenhances the luminance and the lifetime of the organic EL device.

In the invention, an electron-injecting layer which is formed of aninsulator or a semiconductor may further be provided between a cathodeand an organic layer. By providing the layers, current leakage can beeffectively prevented to improve the injection of electrons. As theinsulator, at least one metal compound selected from the groupconsisting of alkali metal calcogenides, alkaline earth metalcalcogenides, halides of alkali metals and halides of alkaline earthmetals can be preferably used. When the electron-injecting layer isformed of the alkali metal calcogenide or the like, the injection ofelectrons can be further improved, it being preferably. Specificallypreferable alkali metal calcogenides include Li₂O, LiO, Na₂S, Na₂Se andNaO and preferable alkaline earth metal calcogenides include CaO, BaO,SrO, BeO, BaS and CaSe. Preferable halides of alkali metals include LiF,NaF, KF, LiCl, KCl and NaCl. Preferable halides of alkaline earth metalsinclude fluorides such as CaF₂, BaF₂, SrF₂, MgF₂ and BeF₂ and halidesother than fluorides.

Examples of the semiconductor for forming an electron-transporting layerinclude oxides, nitrides or oxynitrides containing at least one elementselected from Ba, Ca, Sr, Yb, Al, Ga, In, Li, Na, Cd, Mg, Si, Ta, Sb andZn, and combinations of two or more thereof. The inorganic compound foran electron-transporting layer is preferably a microcrystalline oramorphous insulating thin film. When an electron-transporting layer isformed of the insulating thin film, a more uniform thin film can beformed to reduce pixel defects such as dark spots. Examples of such aninorganic compound include the above-mentioned alkali metalcalcogenides, alkaline earth metal calcogenides, halides of alkalimetals, and halides of alkaline earth metals.

The thickness of electron-injecting or electron-transporting layer isnot particularly limited but preferably 1 to 100 nm.

The first emitting layer or first organic layer which is the organiclayer nearest the anode preferably contains an oxidant. Preferableoxidants contained in the first emitting layer or first organic layerare electron attractors or electron acceptors. Examples thereof includesalts of Lewis acids with various quinone derivatives,dicyanoquinodimethane derivatives and aromatic amines. Particularlypreferred Lewis acids include iron chloride, antimony chloride andaluminum chloride.

The emitting layer of an organic layer nearest the anode or the secondorganic layer preferably contains a reducing agent. Preferable reducingagents are alkali metals, alkaline earth metals, oxides of alkalimetals, oxides of alkaline earth metals, oxides of rare earth metals,halides of alkali metals, halides of alkaline earth metals, halides ofrare earth metals, and complexes formed of alkali metals and aromaticcompounds. Particularly preferred alkali metals are Cs, Li, Na and K.

4. Inorganic Compound Layer

There may be provided an inorganic compound layer(s) in contact with ananode and/or a cathode. The inorganic compound layer functions as anadhesion improving layer. Preferable inorganic compounds used for theinorganic compound layer include alkali metal oxides, alkaline earthmetal oxides, rare earth metal oxides, alkali metal halides, alkalineearth metal halides, rare earth metal halides, and various oxides,nitrides and nitric oxides such as SiO_(x), AlO_(x), SiN_(x), SiON,AlON, GeO_(x), LiO_(x), LiON, TiO_(x), TiON, TaO_(x, TaON, TaN) _(x) andC. As a component of the layer in contact with the anode, SiO_(x),AlO_(x), Sin_(x), SiON, AlON, GeO_(x) and C are preferable, since theycan form a stable injecting interface layer. As a component of the layerin contact with the cathode, LiF, MgF₂, CaF₂, MgF₂ and NaF arepreferable. The thickness of the inorganic compound layer is notparticularly limited, and is preferably 0.1 nm to 100 nm.

Methods of forming respective organic layers including an emitting layerand inorganic compound layers are not particularly limited. For example,known methods such as deposition, spin coating, casting, and LBtechnique can be applied. The electron-injecting layer and the emittinglayer are preferably formed by the same method, because this makes theproperties of the organic EL devices obtained constant and theproduction time can be shortened. For example, when theelectron-injecting layer is formed by deposition, the emitting layer ispreferably formed by deposition, too.

5. Electrodes

For the anode, the following is preferably used: metals, alloys orelectric conductive compounds, or mixtures thereof that have a largework function (e.g., 4 eV or more). Specific examples include indium tinoxide (ITO), indium zinc oxide, tin, zinc oxide, gold, platinum, andpalladium. They can be used individually or as a combination of 2 ormore kinds.

The thickness of the anode is not particularly limited, but ispreferably 10 to 1,000 nm, more preferably 10 to 200 nm.

For the cathode, the following is preferably used: metals, alloys orelectric conductive compounds, or a mixture thereof that have a smallwork function (e.g., less than 4 eV). Specific examples includemagnesium, aluminum, indium, lithium, sodium, and silver. They can beused individually or as a combination of 2 or more kinds. The thicknessof the cathode is not also particularly limited, but is preferably 10 to1,000 nm, more preferably 10 to 200 nm. It is preferred that at leastone of the anode and the cathode be substantially transparent, morespecifically, have a light transmission of 10% or more, in order toeffectively take out light emitted from an emitting layer to theoutside. The electrodes can be formed by vacuum deposition, sputtering,ion plating, electron beam deposition, CVD, MOCVD, plasma CVD and so on.

EXAMPLES

Examples of the invention will be explained below, but the inventionshall not be limited to these Examples. Organic EL devices obtained inExamples were evaluated as follows.

(1) Initial chromaticity: A chromaticity was measured in CIE1931chromaticity coordinates with CS1000 supplied by MINOLTA Co., Ltd.Luminous efficiency was calculated and evaluated.

(2) Luminous efficiency: Calculated from a luminance measured withCS1000 supplied by MINOLTA Co., Ltd. and a current density in themeasurement.

(3) Chromaticity difference between before and after driving: A devicewas driven at a constant current for a constant period of time at roomtemperature, and a chromaticity after the driving was measured in thesame manner as in the measurement of an initial chromaticity.Chromaticity difference=chromaticity after driving−initial chromaticity.An initial luminance in the driving test was set at 1,000 cd/m².

(4) Ionization potential (“IP” hereinafter): Measured in atmosphere witha photoelectron spectrometer (AC-1, supplied by Riken Keiki Co., Ltd.).Photoelectrons released were plotted at ½ fractional power relative tothe energy of ultraviolet ray with which a material (powder) wasirradiated, and the threshold value of photoelectron release energy wastaken as IP.

(5) Affinity level (“Af” hereinafter): Af=Ip−Eg. Eg represents anoptical band gap calculated from a long wavelength side tangent linewhen a solution of a material (solvent: toluene) was measured forultraviolet-visible light absorption spectra with an ultraviolet-visiblelight spectrophotometer (UV-3100PC, supplied by Shimadzu Corporation).

(6) Hole or electron mobility: Measured with TOF-301 supplied by OptelCO. according to a “Time of Flight” method.

Example 1 Formation of Organic EL Device

A 25 mm×75 mm and 1.1 mm thick glass substrate with an ITO transparentelectrode (anode) (supplied by GEOMATEC CO., LTD.) was subjected toultrasonic cleaning in isopropyl alcohol for 5 minutes and thensubjected to UV ozone cleaning for 30 minutes. The cleaned glasssubstrate with transparent electrode lines was fitted to a substrateholder of a vacuum vapor deposition apparatus. First, a 60 nm thick filmofN,N′-bis(N,N′-diphenyl-4-aminophenyl)-N,N-diphenyl-4,4′-diamino-1,1′-biphenyl(to be abbreviated as “TPD232 film” hereinafter) was formed on thesurface thereof on which the transparent electrode lines were formed soas to cover the above transparent electrode. The TPD 232 film worked asa hole injecting layer. The formation of the TPD232 film was followed byformation of 20 nm thick film of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (to be abbreviated as“NPD film” hereinafter) on the TPD232 film. The NPD film worked as ahole transporting layer.

Further, the formation of the NPD film was followed by formation of a 10nm thick film, which was formed by vapor deposition of a styrylderivative DPVDPAN of the formula [32] and B1 of the formula [33] at aweight ratio of 40:1, to obtain a first emitting layer (IP/Af(eV)=5.66/2.73). This first emitting layer emits light in blue. Then, a5 nm thick film of 4,4-N,N-dicarbazolebiphenyl of the formula [34] (tobe abbreviated as “CBP film” hereinafter) was formed. This CBP filmworked as an electron barrier layer (IP/Af [eV]=5.86/2.41). Then, a 30nm thick film was formed by vapor deposition of a styryl derivativeDPVDPAN and R1 of the formula [35] (fluorescence peak wavelength 545 nm)at a weight ratio of 40:1, to obtain a yellow to red emitting layer(Af=2.73). As an electron-transporting layer, a 10 nm thick film oftris(8-quinolinol)aluminum (to be abbreviated as “Alq film” hereinafter)was formed on the above film. Then, Li (Li source: supplied by Saesgetter Co., Ltd.) and Alq were vapor co-deposited to form a 10 nm thickAlq:Li film as an electron-injecting layer. Then, a metal cathode wasformed on this Alq:Li film by vapor deposition of metal Al to athickness of 150 nm, to form an organic EL device. FIG. 5( a) is anenergy level diagram of the electron barrier layer and layers on bothsides thereof in Example 1.

(Evaluation of Organic EL Device)

It was found that the above device had an emission luminance of 100cd/m² at a DC voltage of 6.5 V and an efficiency of 14 cd/A. Light fromthe device made of the materials has CIE1931 chromaticity coordinates of(x,y)=(0.281, 0.281) and was white. When the above device was driven ata constant current at an initial luminance of 1,000 cd/m², the lifetimethereof was excellent 10,000 hours. The chromaticity thereof after10,000 hours' driving was (0.291, 0.290), and the chromaticitydifference between before and after the 10,000 hours' driving was(0.010, 0.009), so that the device was found to be excellent. Table 1shows measurement results of initial performances, lifetime and heatresistance of organic EL devices obtained in Example 1 and the followingExamples 2 to 7 and Comparative Examples 1 to 5. As is clear from thisTable, the organic EL device of this Example had high luminousefficiency and small change in color as compared with conventionaldevices.

Example 2

A device was fabricated in the same manner as in Example 1 except forthe following. A 5 nm thick CzTT film represented by [36] was formed ona first emitting layer to obtain an electron barrier layer (IP/Af(eV)=5.90/2.41). This device had an emission luminance of 103 cd/m² at aDC voltage of 6.5 V and an efficiency of 13 cd/A. The chromaticity was(0.293, 0.282), and white emission was obtained. The chromaticitydifference between before and after 10,000 hours' driving was (0.012,0.011), and it was found that the device had high efficiency and smallchange in chromaticity.

Example 3

A device was fabricated in the same manner as in Example 1 except forthe following. A 2.5 nm thick BCP film represented by [37] was formed ona first emitting layer, followed by formation of a 2.5 nm thick NPD filmrepresented by [38] to obtain an electron barrier layer formed of aplurality of layers (IP of BCP/Af of NPD (eV)=5.93/2.20). This devicehad an emission luminance of 99 cd/m² at a DC voltage of 6.5 V and anefficiency of 16 cd/A. The chromaticity was (0.295, 0.281), and whiteemission was obtained. The chromaticity difference between before andafter 10,000 hours' driving was (0.0082, 0.007), and it was found thatthe device had high efficiency and small change in chromaticity.

Comparative Example 1 Case where the Affinity Level of an ElectronBarrier Layer is Lower than that of an Emitting Layer by 0.08 eV

A device was fabricated in the same manner as in Example 1 except forthe following. A 2.5 nm thick Alq film represented by [39] was formed ona first emitting layer, followed by formation of a 2.5 nm thick Czl filmrepresented by [40] to obtain an electron barrier layer formed of aplurality of layers (IP of Alq/Af of Czl (eV)=5.70/2.65). This devicehad an emission luminance of 101 cd/m² at a DC voltage of 6.5 V and anefficiency of 8 cd/A, which was not satisfactory. The chromaticity was(0.286, 0.283), and white emission was obtained. However, thechromaticity difference between before and after 10,000 hours' drivingwas large as compared with those in Examples 1 to 3.

Comparative Example 2 Case where the Affinity Level of an ElectronBarrier Layer is Equivalent to that of an Emitting Layer

A device was fabricated in the same manner as in Example 1 except forthe following. A 5 nm thick DPVDPAN film was formed on a first emittinglayer to obtain a non-doped layer (IP/Af (eV)=5.66/2.73) that did notwork as an electron barrier layer. This device had an emission luminanceof 100 cd/m² at a DC voltage of 6.5 V and an efficiency of 6 cd/A, whichwas not satisfactory. The chromaticity was (0.280, 0.282), and whiteemission was obtained. However, the chromaticity difference betweenbefore and after 10,000 hours' driving was large as compared with thosein Examples 1 to 3. FIG. 5( b) shows an energy level diagram of theelectron barrier layer and layers on both sides thereof in ComparativeExample 2.

Comparative Example 3 Case where the Affinity Level of an ElectronBarrier Layer is Greater than that of an Emitting Layer

A device was fabricated in the same manner as in Example 1 except forthe following. A 5 nm thick TZA film represented by [41] was formed on afirst emitting layer to obtain an electron barrier layer (IP/Af(eV)=6.30/2.88). This device had an emission luminance of 98 cd/m² at aDC voltage of 8.5 V and an efficiency of 9 cd/A. The chromaticity was(0.281, 0.282), and white emission was obtained. However, thechromaticity difference between before and after 10,000 hours' drivingwas very large as compared with those in Examples 1 to 3. FIG. 5( c)shows an energy level diagram of the electron barrier layer and layerson both sides thereof in Comparative Example 3.

Comparative Example 4 Case where the Ionization Potential of an ElectronBarrier Layer is Smaller than that of a First Emitting Layer

A device was fabricated in the same manner as in Example 1 except forthe following. A 5 nm thick TCTA film represented by [42] was formed ona first emitting layer to obtain an electron barrier layer (IP/Af(eV)=5.63/2.28). This device had an emission luminance of 105 cd/m² at aDC voltage of 7.0 V and an efficiency of 7 cd/A. The chromaticity was(0.283, 0.281), and white emission was obtained. However, thechromaticity difference between before and after 10,000 hours' drivingwas very large as compared with those in Examples 1 to 3. FIG. 5( d)shows an energy level diagram of the electron barrier layer and layerson both sides thereof in Comparative Example 4.

Comparative Example 5 Case where No Electron Barrier Layer is Present

A device was fabricated in the same manner as in Example 1 except forthe following. A second emitting layer was formed on a first emittinglayer, and no electron barrier layer was formed. The chromaticity ofthis device was (0.282, 0.281), and white emission was obtained.However, the chromaticity difference between before and after 10,000hours' driving was very large as compared with those in Examples 1 to 3.

Example 4

A 25 mm×75 mm and 1.1 mm thick glass substrate with an ITO transparentelectrode (anode) (supplied by GEOMATEC CO., LTD.) was subjected toultrasonic cleaning in isopropyl alcohol for 5 minutes and thensubjected to UV ozone cleaning for 30 minutes. The cleaned glasssubstrate with transparent electrode lines was fitted to a substrateholder of a vacuum vapor deposition apparatus. First, a 60 nm thick TPD232 film was formed on the surface thereof on which the transparentelectrode lines were formed so as to cover the above transparentelectrode. The TPD 232 film worked as a hole injecting layer. Theformation of the TPD232 film was followed by formation of 20 nm thickNPD film on the TPD232 film. The NPD film worked as a hole transportinglayer.

Further, the formation of the NPD film was followed by formation of a 10nm thick film, which was formed by vapor deposition of a styrylderivative DPVDPAN of the formula [32] and B1 of the formula [33] at aweight ratio of 40:1, to obtain a first emitting layer (IP/Af(eV)=5.66/2.73). This first emitting layer emits light in blue. Then, a5 nm thick titanium oxide film was formed. This titanium oxide filmworked as an electron barrier layer (IP/Af (eV)=6.21/2.01). Then, a 30nm thick film was formed by vapor deposition of a styryl derivativeDPVDPAN and R1 (fluorescence peak wavelength 545 mm) of the formula [35]at a weight ratio of 40:1, to obtain a yellow to red emitting layer(Af=2.73). On this film was formed a 10 nm thick Alq film as anelectron-transporting layer. Then, Li (Li source: supplied by Saesgetter Co., Ltd.) and Alq were vapor co-deposited to form a 10 nm thickAlq:Li film as an electron-injecting layer. Then, a metal cathode wasformed on this Alq:Li film by vapor deposition of metal Al to athickness of 150 nm, to form an organic EL device.

It was found that the above device had an emission luminance of 100cd/m² at a DC voltage of 6.5 V and an efficiency of 13 cd/A. Light fromthe device made of the materials has CIE1931 chromaticity coordinates of(x,y)=(0.282, 0.280) and was white. The chromaticity difference betweenbefore and after the 10,000 hours' driving was (0.011, 0.012), so thatthe device was found to be excellent. The organic EL device of thisExample had high luminous efficiency and small change in color ascompared with conventional devices. Further, when the titanium oxide wasreplaced with germanium oxide, silicon oxide or lithium fluoride, equalperformances were obtained.

Example 5

A 25 mm×75 mm and 1.1 mm thick glass substrate with an ITO transparentelectrode (anode) (supplied by GEOMATEC CO., LTD.) was subjected toultrasonic cleaning in isopropyl alcohol for 5 minutes and thensubjected to UV ozone cleaning for 30 minutes. The cleaned glasssubstrate with transparent electrode lines was fitted to a substrateholder of a vacuum vapor deposition apparatus. First, a 60 nm thick TPD232 film was formed on the surface thereof on which the transparentelectrode lines were formed so as to cover the above transparentelectrode. The TPD 232 film worked as a hole injecting layer. Theformation of the TPD232 film was followed by formation of 20 nm thickNPD film on the TPD232 film. The NPD film worked as a hole transportinglayer.

Further, the formation of the NPD film was followed by formation of a 10nm thick film, which was formed by vapor deposition of a styrylderivative DPVDPAN of the formula [32] and B1 of the formula [33] at aweight ratio of 40:1, to obtain a first emitting layer (IP/Af(eV)=5.66/2.73). This first emitting layer emits light in blue. Then, a5 nm thick CPB film represented by [34] was formed. This CPB film workedas an electron barrier layer (IP/Af (eV)=5.86/2.41). Then, a 30 nm thickfilm was formed by vapor deposition of a carbazole derivative of theformula [43] and an iridium complex of the formula [44] at a weightratio of 30:1.5, to obtain a red emitting layer (Af (eV)=2.55). On thisfilm was formed a 10 nm thick tris(8-quinolinol)aluminum film (to beabbreviated as “Alq film” hereinafter) as an electron-transportinglayer. Then, Li (Li source: supplied by Saes getter Co., Ltd.) and Alqwere vapor co-deposited to form a 10 nm thick Alq:Li film as anelectron-injecting layer. Then, a metal cathode was formed on thisAlq:Li film by vapor deposition of metal Al to a thickness of 150 nm, toform an organic EL device.

It was found that the above device had an emission luminance of 101cd/m² at a DC voltage of 8.5 V and an efficiency of 12 cd/A. Light fromthe device made of the materials has CIE1931 chromaticity coordinates of(x,y)=(0.301, 0.281) and was white. When this device was driven at aconstant current at an initial luminance of 1,000 cd/m², the lifetimethereof was excellent 5,000 hours. The chromaticity thereof after 5,000hours' driving was (0.287, 0.266), and the chromaticity differencebetween before and after the 5,000 hours' driving was (−0.014, −0.015),so that the device was found to be excellent. The organic EL device ofthis Example had high luminous efficiency and small change in color ascompared with conventional devices.

Example 6

A 25 mm×75 mm and 1.1 mm thick glass substrate with an ITO transparentelectrode (anode) (supplied by GEOMATEC CO., LTD.) was subjected toultrasonic cleaning in isopropyl alcohol for 5 minutes and thensubjected to UV ozone cleaning for 30 minutes. The cleaned glasssubstrate with transparent electrode lines was fitted to a substrateholder of a vacuum vapor deposition apparatus. First, a 60 nm thick TPD232 film was formed on the surface thereof on which the transparentelectrode lines were formed so as to cover the above transparentelectrode. The TPD 232 film worked as a hole injecting layer. Theformation of the TPD232 film was followed by formation of 20 nm thickNPD film on the TPD232 film. The NPD film worked as a hole transportinglayer.

Further, the formation of the NPD film was followed by formation of a 10nm thick film, which was formed by vapor deposition of a styrylderivative DPVDPAN of the formula [32] and B1 of the formula [33] at aweight ratio of 40:1, to obtain a first emitting layer (IP/Af(eV)=5.66/2.73). This first emitting layer emits light in blue. Then, a5 nm thick film was formed by vapor deposition of CBP represented by[34] and an iridium complex of the formula [44] at a weight ratio of30:1.5, to obtain an electron blocking and red emitting layer (IP/Af(eV)=5.86/2.41). Then, a 30 nm thick film was formed by vapor depositionof a carbazole derivative of the formula [42] and an iridium complex ofthe formula [45] at a weight ratio of 30:1.5, to obtain a green emittinglayer (Af (eV)=2.55). On this film was formed a 10 nm thicktris(8-quinolinol)aluminum film (to be abbreviated as “Alg film”hereinafter) as an electron-transporting layer. Then, Li (Li source:supplied by Saes getter Co., Ltd.) and Alq were vapor co-deposited toform a 10 nm thick Alq:Li film as an electron-injecting layer. Then, ametal cathode was formed on this Alq:Li film by vapor deposition ofmetal Al to a thickness of 150 nm, to form an organic EL device.

It was found that the above device had an emission luminance of 95 cd/m²at a DC voltage of 8.5 V and an efficiency of 13 cd/A. Light from thedevice made of the materials has CIE1931 chromaticity coordinates of(x,y)=(0.300, 0.295) and was white. When this device was driven at aconstant current with an initial luminance of 1,000 cd/m², the lifetimethereof was 6,000 hours, and the device was excellent. The chromaticitythereof after 6,000 hours' driving was (0.289, 0.282), and thechromaticity difference between before and after the 6,000 hours'driving was (−0.011, −0.013), so that the device was found to beexcellent. The organic EL device of this Example had high luminousefficiency and small change in color as compared with conventionaldevices.

Example 7

A 25 mm×75 mm and 1.1 mm thick glass substrate with an ITO transparentelectrode (anode) (supplied by GEOMATEC CO., LTD.) was subjected toultrasonic cleaning in isopropyl alcohol for 5 minutes and thensubjected to UV ozone cleaning for 30 minutes. The cleaned glasssubstrate with transparent electrode lines was fitted to a substrateholder of a vacuum vapor deposition apparatus. First, a 60 nm thickTPD232 film was formed on the surface thereof on which the transparentelectrode lines were formed so as to cover the above transparentelectrode. The TPD 232 film worked as a hole injecting layer. Theformation of the TPD232 film was followed by formation of 20 nm thickNPD film on the TPD232 film. The NPD film worked as a hole transportinglayer.

Further, the formation of the NPD film was followed by formation of a 10nm thick film, which was formed by vapor deposition of4,4′-bis(2,2-diphenylvinyl)biphenyl (DPVBi) (hole mobility: 8×10⁻⁴cm²/v·s) of the formula [46] and 4,4′-bis(diphenylamino)stilbene (DPAVB)of the formula [47] at a weight ratio of 40:1, to obtain a firstemitting layer (IP/Af (eV)=5.65/2.57). This first emitting layer emitslight in blue. Then, a 5 nm thick CBP film represented by [34] wasformed. This CBP film worked as an electron barrier layer (IP/Af(eV)=5.86/2.41). Then, a 30 nm thick film was formed by vapor depositionof Alq (electron mobility: 1×10⁻⁶ cm²/v·s) of the formula [39] and R1(fluorescence peak wavelength 545 nm) of the formula [35] at a weightratio of 40:1, to obtain a yellow to red emitting layer (Af (eV)=3.00).On this film was formed a 10 nm thick Alq film as anelectron-transporting layer. Then, Li (Li source: supplied by Saesgetter Co., Ltd.) and Alq were vapor co-deposited to form a 10 nm thickAlq:Li film as an electron-injecting layer. Then, a metal cathode wasformed on this Alq:Li film by vapor deposition of metal Al to athickness of 150 nm, to form an organic EL device.

It was found that the above device had an emission luminance of 99 cd/m²at a DC voltage of 6.5 V and an efficiency of 11 cd/A. Light from thedevice made of the materials has CIE1931 chromaticity coordinates of(x,y)=(0.298, 0.305) and was white. When this device was driven at aconstant current at an initial luminance of 1,000 cd/m², the lifetimethereof was excellent 10,000 hours. The chromaticity thereof after10,000 hours' driving was (0.308, 0.317), and the chromaticitydifference between before and after the 10,000 hours' driving was(0.010, 0.012), so that the device was found to be excellent. Theorganic EL device of this Example had high luminous efficiency and smallchange in color as compared with conventional devices.

TABLE 1 [46]

[47]

IP/Af in the IP/Af in the Af in the first emitting electron secondemitting Luminous Chromaticity change layer barrier layer layer Initialefficiency after 10,000 hours' (eV) (eV) (eV) chromaticity (cd/A)driving Example 1 5.66/2.73 5.86/2.41 2.73 (0.281, 0.281) 14 (0.010,0.009) (DPVDPAN:B1) (CBP) (DPVDPAN:R1) Example 2 5.66/2.73 5.90/2.412.73 (0.293, 0.282) 13 (0.012, 0.011) (CzTT) Example 3 5.66/2.735.93/2.20 2.73 (0.295, 0.281) 16 (0.008, 0.007) (BCP/NPD) Comparative5.66/2.73 5.70/2.65 2.73 (0.286, 0.283) 8 (0.018, 0.022) example 1(Alq/Czl) Comparative 5.66/2.73 5.66/2.73 2.73 (0.280, 0.282) 6 (0.016,0.020) example 2 (DPVDPAN) Comparative 5.66/2.73 6.30/2.88 2.73 (0.281,0.282) 9 (0.036, 0.052) Example 3 (TAZ) Comparative 5.66/2.73 5.63/2.282.73 (0.283, 0.281) 7 (0.042, 0.048) example 4 (TCTA) Comparative5.66/2.73 (none) 2.73 (0.282, 0.281) 7 (0.015, 0.015) example 5 Example4 5.66/2.73 6.21/2.01 2.73 (0.282, 0.280) 13 (0.011, 0.012) (TiO₂)Example 5 5.66/2.73 5.86/2.41 2.55 (0.301, 0.281) 12  (−0.014, −0.015)*(CBP) ([43]:[44]) Example 6 5.66/2.73 5.86/2.41 2.55 (0.300, 0.295) 13 (−0.011, −0.013)* (CBP:[44]) ([42]:[45]) Example 7 5.65/2.57 5.86/2.413.00 (0.298, 0.305) 11 (0.010, 0.012) (DPVBi:DPAVB) (CBP) (Alq:R1)*Chromaticity change after 5,000 hours' driving in Example 5,Chromaticity change after 6,000 hours' driving in Example 6

INDUSTRIAL UTILITY

The organic EL device of the invention has high luminous efficiency andhas little change in chromaticity, so that it can be applied to variousdisplays (such as commercial and industrial displays, specifically,various mono-color or full color displays such as a cellular phone, PDA,an automobile navigation system, TV, etc.), various illumination(backlight, etc.) and the like.

1. An organic electroluminescent device comprising in sequence an anode,a first emitting layer, a first carrier barrier layer, a second carrierbarrier layer, a second emitting layer and a cathode stacked, wherein anionization potential of the first carrier barrier layer is more than theionization potential of the first emitting layer by 0.1 eV or more andan affinity level of the second carrier barrier layer is less than theaffinity level of the second emitting layer by 0.1 eV or more.
 2. Theorganic electroluminescent device according to claim 1, wherein theionization potential of the first carrier barrier layer is more than theionization potential of the first emitting layer by 0.2 eV or more andthe affinity level of the second carrier barrier layer is less than theaffinity level of the second emitting layer by 0.2 eV or more.
 3. Theorganic electroluminescent device according to claim 1, wherein thefirst emitting layer comprises a first dopant for a first emission colorand the second emitting layer comprises a second dopant for a secondemission color.
 4. The organic electroluminescent device according toclaim 3, wherein at least one carrier barrier layer comprises a thirddopant for a third emission color.
 5. The organic electroluminescentdevice according to claim 4, wherein the first, second and third dopantsare selected from the group consisting of blue, green and red.
 6. Theorganic electroluminescent device according to claim 1, wherein thefirst emitting layer emits blue or red light.
 7. The organicelectroluminescent device according to claim 1, wherein the secondemitting layer emits blue or red light.
 8. The organicelectroluminescent device according to claim 1, wherein one of the firstemitting layer and the second emitting layer emits blue light, andanother emitting layer emits red light.
 9. The organicelectroluminescent device according to claim 1, wherein the firstemitting layer comprises a hole-transporting material and the secondemitting layer comprises an electron-transporting material.